Electro-conductive oxides and electrodes using the same

ABSTRACT

Electro-conductive oxides showing excellent electro-conductivity, electrodes using the electro-conductive oxide and methods for manufacturing the same are described. The electro-conductive oxides are represented by the general formula: 
     
         M(1).sub.x M(2).sub.y In.sub.z 
    
      O.sub.(x+.spsb.3 y/ .spsb.2 + .spsb.3 z/ .spsb.2.sub.)-d. 
     The above electro-conductive oxides show not only excellent electro-conductivity but also excellent transparency all over the visible region and therefore they are particularly useful as, for example, electrodes for liquid crystal displays, EL displays and solar cells, which require light transmission.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electro-conductive oxide showingexcellent electro-conductivity, an electrode using theelectro-conductive oxide and a method for manufacturing the same. Theelectro-conductive oxides of the present invention show not onlyexcellent electro-conductivity but also excellent transparency all overthe visible region and therefore they are particularly useful as, forexample, electrodes for displays and solar cells, which require lighttransmission.

2. Related Art

Transparent electro-conductive materials, which are transparent in thevisible region and electro-conductive, are widely used as transparentelectrodes of various panel form displays such as liquid crystaldisplays and EL displays and transparent electrodes of solar cells. Theyare also used as defogging heaters of chilled show cases, heat rayreflecting films for window glasses of buildings and automobiles,anti-static coatings or electromagnetic wave shields of transparentarticles and the like.

As transparent electro-conductive materials, generally used are metaloxide semi-conductors. Various metal oxide materials are proposed andexamples thereof include tin oxide (SnO₂), indium oxide doped with tin(ITO), Cd₂ SnO₄ and CdIn₂ O₄.

Transparency of such transparent electro-conductive materials relates tothe fundamental absorption edge wavelength. The term "fundamentalabsorption edge wavelength" means a wavelength at which light absorbanceof the material due to electron transition from a valence band to aconduction band begins to appear. The fundamental absorption edgewavelength may be determined by the reflection method or thetransmission method using a spectrophotometer. ITO has its absorptionedge around 450 nm and does not absorb light of a wavelength longer thanthat wavelength. Therefore, it is transparent substantially all over thevisible region except for the short wavelength region. On the otherhand, it has a carrier concentration comparable to that of metals and acarrier mobility relatively large as an oxide and so it has a highelectro-conductivity more than 1000 S/cm. Therefore, among theabove-mentioned materials, ITO is particularly widely used.

Various panel form displays are widely used for various electricappliances including telephones, laundry machines, rice cookers, gamemachines, portable televisions, computers and wordprocessors. Inparticular, in note-book type personal computers, word-processors andthe like, large panel form displays having a diagonal length of about 10inches have become prevalent. In addition, researches of further largerpanel form displays are continued for use in wall-televisions and thelike.

Hitherto, ITO has been used also for transparent electrodes of panelform displays. However, as described hereinbefore, ITO has itsfundamental absorption edge wavelength of 450 nm and hence shows poortransparency in the short wavelength region of the visible region (lessthan 450 nm). Therefore, since a larger thickness of ITO electrodescause their coloration, a thinner thickness has been preferred. On theother hand, a larger thickness is preferred from the view point ofreduction of electric resistance, i.e., reduction of power consumption.Therefore, a suitable thickness of transparent electrodes has beenselected considering their transparency and electric resistance.

However, transparent electrodes for panel form displays of a larger sizehave a longer distance between the ends of the electrode surface andhence electric resistance between the ends is increased. In addition,displays of higher resolution must have a smaller line width oftransparent electrodes and this also leads to higher resistance. On theother hand, if the electrode thickness is made larger to decreaseelectric resistance, it may cause practically unacceptable coloration.That is, conventional ITO practically used so far as materials fortransparent electrodes as it is cannot provide large transparentelectrodes having both satisfactory transparency andelectro-conductivity.

For these reasons, it has been desired to develop materials showingtransparency in a short wavelength region of the visible region, i.e.,shorter than 450 nm, and high electro-conductivity.

For example, a spinel compound, ZnGa₂ O₄, was reported as a materialhaving its absorption edge in the short wavelength region below 450 nm,and ZnGa₂ O₄ shows its absorption edge at 250 nm. However, it shows lowelectro-conductivity as low as 30 S/cm (The Ceramic Association ofJapan, Preprints p585, (1993)).

A trirutile type compound, CdSb₂ O₆, has also been known. CdSb₂ O₆ showsits absorption edge at 350 nm. However, it also shows lowelectro-conductivity as low as 40 S/cm (The 54th Congress of the Societyof Applied Physics, Preprints, vol. 2, p502).

That is, there has been known no materials having an absorption edge ata wavelength shorter than 450 nm and showing electro-conductivitycomparable to or higher than that of ITO.

Therefore, the object of the present invention is to provide novelmaterials which do not cause coloration even with a thickness largerthan that of conventional ITO films because they have an absorption edgeat a wavelength shorter than 450 nm and show electro-conductivitycomparable to or higher than that of ITO.

Another object of the present invention is to provide electrodescomprising the above-mentioned novel materials, which are useful forliquid crystal displays, EL displays, solar cells and the like.

SUMMARY OF THE INVENTION

According to the first aspect of the present invention, there isprovided an electro-conductive oxide represented by the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is at least one element selected from the group consistingof magnesium and zinc, M(2) is at least one element selected from thegroup consisting of aluminium and gallium, the ratio (x:y) is within arange of 0.2 to 1.8:1, the ratio (z:y) is within a range of 0.4 to 1.4:1and the oxygen deficit amount (d) is within a range of 3×10⁻⁵ to 1×10⁻¹times the value of (x+3y/2+3z/2) (first embodiment of the presentinvention).

According to the second aspect of the present invention, there isprovided an electro-conductive oxide represented by the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is at least one element selected from the group consistingof magnesium and zinc, M(2) is at least one element selected from thegroup consisting of aluminium and gallium, the ratio (x:y) is within arange of 0.2 to 1.8: 1, the ratio (z:y) is within a range of 0.4 to1.4:1 and the oxygen deficit amount (d) is within a range of from 0 to1×10⁻¹ times the value of (x+3y/2+3z/2), in which a part of at least oneof M(1), M(2) and In is replaced with one or more other elements and theelements replacing M(1) are of di- or higher valence and the elementsreplacing M(2) and In are of tri- or higher valence (the secondembodiment of the present invention).

In addition, according to the third aspect of the present invention,there is provided an electro-conductive oxide represented by the generalformula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is at least one element selected from the group consistingof magnesium and zinc, M(2) is at least one element selected from thegroup consisting of aluminium and gallium, the ratio (x:y) is within arange of 0.2 to 1.8:1, the ratio (z:y) is within a range of 0.4 to 1.4:1and the oxygen deficit amount (d) is within a range of from 0 to 1×10⁻¹times the value of (x+3y/2+3z/2), which is implanted with cations (thethird embodiment of the present invention).

The present invention also provides electrodes consisting of antransparent substrate and an electro-conductive layer provided on atleast a part of at least one surface of the substrate, wherein theelectro-conductive layer comprises an electro-conductive oxide accordingto any one of the above-mentioned first to third embodiments of theinvention.

In the electrodes of the present invention, it is particularly preferredthat the electro-conductive layer comprises an electro-conductive oxideand faces (00n), where n is a positive integer, of the aboveelectro-conductive oxide are oriented in substantially parallel with thesurface of the transparent substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an atomic model of the octahedral structure of InO₆ wherewhite circles represent In atoms and black circles represent oxygenatoms, wherein FIG. 1A is a view from a direction perpendicular to thefaces (00n) and FIG. 1B is a view from a direction parallel with thefaces (00n).

FIG. 2 shows a schematic view of the relation of octahedrons of InO₆,faces (00n) of the octahedrons and the substrate.

FIG. 3 shows routes for electrons being linear in oriented films andbeing zigzag in non-oriented films.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be further explained hereinafter.

Electro-conductive oxides according to the first embodiment of theinvention

In the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d,

M(1) is at least one element selected from magnesium and zinc.Therefore, M(1) may be either magnesium or zinc alone, or magnesium andzinc may coexist as M(1). When magnesium and zinc coexist, the ratio ofmagnesium and zinc is not particularly limited. However, when magnesiumis increased, the absorption edge is sifted to a shorter wavelength andhence transparency is enhanced. When zinc is increased,electro-conductivity is enhanced.

M(2) may be either aluminium or gallium alone, or aluminium and galliummay coexist as M(2). When aluminium and gallium coexist, the ratio ofaluminium and gallium is not particularly limited. However, whenaluminium is increased, the crystallization temperature becomes higher.When gallium is increased, the crystallization temperature becomeslower.

The ratio (x:y) should be in the range of 0.2 to 1.8:1 and, when x/y isbelow 0.2, deposition of InGaO₃ phase is significant and thuselectro-conductivity is lowered. When x/y exceeds 1.8, crystallinestructure becomes unstable. The ratio (x:y) is preferably in the rangeof 0.3 to 1.6:1, more preferably, in the range of 0.4 to 1.3:1.

The ratio (z:y) should be in the range of 0.4 to 1.4:1 and, when z/y isbelow 0.4, deposition of ZnGa₂ O₄ phase and the like is significant andthus electro-conductivity is lowered. When z/y exceeds 1.4, In₂ O₃ phaseis deposited and transparency is deteriorated. The ratio (z:y) ispreferably in the range of 0.6 to 1.4:1, more preferably, in the rangeof 0.8 to 1.2:1.

The oxygen deficit amount (d) should be in the range of 3×10⁻⁵ to 1×10⁻¹times the value of (x+3y/2+3z/2). In general, if the oxygen deficitamount (d) is too small, electro-conductivity is unduly lowered and,when it is too large, transparency is unduly deteriorated due toabsorption of visible lights.

When the oxygen deficit amount (d) is below 3×10⁻⁵ times the value of(x+3y/2+3z/2), electro-conductivity becomes too low and is notpractically acceptable. On the other hand, when the oxygen deficitamount (d) exceeds 3×10⁻¹ times the value of (x+3y/2+3z/2), the materialbegins to absorb visible rays and it is not preferred. The oxygendeficit amount (d) is preferably in the range of 1×10⁻³ to 1×10⁻¹ timesthe value of (x+3y/2+3z/2), more preferably, in the range of 1×10⁻² to1×10⁻¹ times the value of (x+3y/2+3z/2).

The term "oxygen deficit amount" means a value obtained by subtractingnumber of oxygen ions contained in 1 mol of oxide crystalline from thestoichiometric amount of the ions, which is expresses in the mol unit.The number of oxygen ions contained in oxide crystals can be determinedby measuring the amount of carbon dioxide produced by heating the oxidecrystals in carbon powder through infrared absorption spectrum analysis.The stoichiometric number of oxygen ions can be calculated from the massof oxide crystals.

When the amount of carrier electrons in conduction bands is in a certainrange, the oxides of the present invention show goodelectro-conductivity. Such an amount of carrier electrons is in therange of from 1×10¹⁸ /cm³ to 1×10²² /cm³, preferably from 1×10¹⁹ /cm³ to5×10²¹ /cm³.

The amount of carrier electrons may be determined by the van der Pauwmethod electro-conductivity measurement apparatus.

As specific examples of oxides of the first embodiment, there can bementioned electro-conductive oxides represented by the general formula:In₂ Ga₂ ZnO_(7-d) and have an oxygen deficit amount (d) of from 2.1×10⁻⁴to 0.7. When the oxygen deficit amount (d) is below 2.1×10⁻⁴,electro-conductivity becomes too low and practically usefulelectro-conductivity cannot be obtained. On the other hand, oxygendeficit amount (d) exceeding 0.7 is not preferred since visible raysbegin to be absorbed. The oxygen deficit amount (d) is preferably in therange of from 7×10⁻³ to 0.7, more preferably, from 7×10⁻² to 0.7.

With respect to the oxides represented by the general formula: In₂ Ga₂ZnO_(7-d), there have been the following three reports all of which aredirected to the oxides where d is 0.

In the first two reports, Kimizuka et al. analyzed crystallinestructures of the oxides represented by the general formula: In₂ Ga₂ZnO₇ (K. Kato, I. Kawada, N. Kimizuka and T. Katsura, Z. Kristallogr.vol. 143, p278, (1976) and N. Kimizuka, T. Mohri, Y. Matsui and K.Shiratori, J. Solid State Chem., vol.74, p98 (1988)).

Kimizuka et al. synthesized the oxides represented by the generalformula: In₂ Ga₂ ZnO₇ from In₂ O₃, Ga₂ O₃ and ZnO, and obtained theirpowder X-ray diffraction data to reveal that they have a Yb₂ Fe₃ O₇ formstructure. According to Kimizuka et al., Yb₂ Fe₃ O₇ comprises YbO₁.5layers (U layers), Fe₂ O₂.5 layers (T layers) and Fe₂ O₁.5 layers (Vlayers). The U layer is formed from three layers of a Yb layer andoxygen layers on and under the Yb layer. The T layer and the V layer areformed from Fe and oxygen locating in substantially the same plane. Yb₂Fe₃ O₇ is a crystal formed from three types of layers, U, T and V,stacked in the order of U, T, T, U, V, U, T, T, U, V, U. Upon the Tlayers and the U layers are stacked, coulomb energy is minimized becausecation layers are placed on anions arrayed in triangles and thereby adipyramid structure in three-fold symmetry is formed. In the oxidesrepresented by the general formula: In₂ Ga₃ ZnO₇, Yb sites of the Ulayers are occupied by In, Fe sites of the T layers are occupied by Gaand Zn in a ratio of 1:1, and the Fe sites of the V layers are occupiedby Ga.

The third report includes the results of the analysis of the relationsbetween In₂ Ga₂ ZnO₇, ZnGa₂ O₄ and ZnO phases at 1350° C. (M. Nakamura,N. Kimizuka and T. Mohri, J. Solid State Chem. vol. 93 (2), p298(1991)).

The above-mentioned reports are, to the present inventors' knowledge,all of the reports which has been made on the oxides represented by thegeneral formula: In₂ Ga₂ ZnO₇ up to now. All of these reports did notconsider the oxygen deficit amount and the oxides were not subjected toany treatment to cause the oxygen deficit. In contrast, the specificexamples of the first embodiment of the present invention, representedby the general formula: In₂ Ga₂ ZnO_(7-d), are electro-conductive oxideshaving an oxygen deficit amount (d) of from 2.1×10⁻⁴ to 0.7.

Other specific examples of the oxides according to the first embodimentare those represented by the general formula: M(1)M(2) InO₄ and havingan oxygen deficit amount (d) of from 1.2×10⁻⁴ to 0.4. Some of the oxidesof the general formula: M(1)M(2)InO₄ have been already known. However,all of those known oxides have no oxygen deficit. In contrast, theelectro-conductive oxides of the present invention has an oxygen deficitamount (d) of 1.2×10⁻⁴ to 0.4 and therefore they are novel materials.

As the published research reports of the materials represented by thegeneral formula: M(1)M(2)InO4, there can be mentioned, for example, thereport of V. A. Kutoglu et al. which describes crystalline structures ofMgAlInO₄ and MgGaInO₄ (Z. Anorg. Allg. Chem., vol. 456, p130-146(1979)). According to this report, both of MgAlInO₄ and MgGaInO₄ have amonoclinic structure in which layers of oxygen in six-fold symmetry arestacked in the order of ababcacabcbc, and Mg and Al (or Ga) are locatedat the centers of deformed dipyramids in three-fold symmetry formed fromoxygen. Indium has its coordination number of 6, and forms layers infourfold symmetry between the oxygen layers. N. Kimizuka et al. laterconfirmed that MgGaInO₄ has this crystalline structure and termed YbFe₂O₄ form structure (J. Solid State Chem., vol. 60, p382-384 (1985)).

G. Blasse et al. reported the fluorescent properties of MgGaInO₄ (Mat.Res. Bull. vol. 21, p1057-1062). According to this report, MgGaInO₄ doesnot radiate fluorescence at room temperature, but it radiates orangefluorescence when it is irradiated with ultraviolet rays at 250K orlower. It has wide luminescence and absorption spectra bands to a lowtemperature as low as 5K and it has an absorption band of from 240 nm to400 nm with the center of 310 nm and a luminescence band of from 450 nmto 700 nm or more with the center of 550 nm at 5K. From these results,G. Blasse et al. assumed that the bands spread two-dimensionally andupper part of the valence electron band and lower part of the conductionband are formed from the In layer and the oxygen layers on its bothsides. However, this report does not refer to the location of theabsorption band at room temperature at all.

As mentioned above, several reports on the materials represented by thegeneral formula: M(1)M(2)InO₄ have been published so far. However, noneof them refers to their transparency and electro-conductivity, and thusnone of them tried to use M(1)M(2) InO₄ as transparentelectro-conductive materials.

Under the circumstances described above, the present inventors have beenfound that MgGaInO₄ has an absorption edge wavelength of around 330 nmand shows transparency all over the visible region, the conduction bandcan be implanted with electrons and therefore it can showelectro-conductivity by implanting electrons into the conduction bands.In addition, it is found that the above-described optical properties andelectro-conductivity of MgGaInO₄ can be obtained even though a part orall of its Mg sites are replaced with Zn and a part or all of its Gasites are replaced with Al.

The electro-conductive oxide of the present invention represented by thegeneral formula:

    M(1)M(2)InO.sub.4.sbsb.-d

can be also represented by the general formula:

    Mg.sub.a Zn.sub.1.sbsb.-a Al.sub.b Ga.sub.1.sbsb.-b InO.sub.4.sbsb.-d

wherein a is 0 to 1 and b is 0 to 1.

Specific examples of the electro-conductive oxides of the presentinvention represented by Mg_(a) Zn₁.sbsb.-a Al_(b) Ga₁.sbsb.-bInO₄.sbsb.-d are, for example, MgAlInO₄.sbsb.-d, ZnAlInO₄.sbsb.-d,MgGaInO₄.sbsb.-d, ZnGaInO₄.sbsb.-d, Mg_(a) Zn₁.sbsb.-a AlInO_(4-d),Mg_(a) Zn₁.sbsb.-31 a GaInO_(4-d), MgAl_(b) Ga_(1-b) InO_(4-d) andZnAl_(b) Ga₁.sbsb.-b InO₄.sbsb.-d. The values of a and b in the formulaecan be suitably selected by considering optical properties andelectro-conductivity required for the electro-conductive oxidesdepending on their compositions.

The above-described electro-conductive oxides should have an oxygendeficit amount (d) of from 1.2×10⁻⁴ to 0.4. Because of the oxygendeficit amount in this range, there can be provided materials which canbe suitably used as electrodes and the like. The oxygen deficit amount(d) is, from the view point of good balance of electro-conductivity andtransparency, preferably in the range of from 4×10⁻³ to 0.4, morepreferably from 4×10⁻² to 0.4.

Electro-conductive oxides according to the second embodiment of theinvention

As to the electro-conductive oxides according to the second embodimentof the invention, the descriptions for the electro-conductive oxidesaccording to the first embodiment of the invention hereinbefore abouttheir M(1), M(2), the ratio (x:y) and the ratio (z:y) in the generalformula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

can be applied.

Further, in the electro-conductive oxides according to the secondembodiment of the invention, a part of at least one of M(1), M(2) and Inis replaced with one or more other elements and the elements replacingM(1) are of di- or higher valence and the elements replacing M(2) and Inare of tri- or higher valence. By replacing a part of at least one ofM(1), M(2) and In with one or more other elements, it is possible toimplant electrons into the oxides.

In the electro-conductive oxides according to the second embodiment ofthe invention, in addition to the introduction of oxygen deficit, thereplacement of a part of the metal ions with other metal ions to implantcarrier electrons into the conduction band can provideelectro-conductivity.

Mg and Zn used for M(1) are divalent elements and so elements capable ofreplacing them are divalent elements or elements of higher valence. Asthe valence of elements becomes higher, larger amount of carrier can beimplanted with the same amount. Valence of elements which can be usedfor the replacement is normally di-, tri-, tetra-, penta- orhexavalence.

Examples of the elements of divalence or higher valence are, forexample, Be, Mg, Ca, Sr, Ba, Cd, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni,Zn, Ga, Ge, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, In, Sn, Sb, La, Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt,Tl, Pb, Bi and Po.

Al and Ga used for M(2) and In are trivalent elements and so elementscapable of replacing them are trivalent elements or elements of highervalence. As the valence of elements becomes higher, larger amount ofcarrier can be implanted with the same amount. Valence of elements whichcan be used for the replacement is normally tri-, tetra-, penta- orhexavalence.

Examples of the elements of trivalence or higher valence are, forexample, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Ge, Y, Zr, Nb, Mo,Tc, Ru, Rh, Pd, In, Sn, Sb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Tl, Pb, Bi and Po.

As described above, by replacing a part of M(1), M(2) and/or In withelements such as those mentioned above, carrier electrons are implantedinto conduction bands. The suitable amount of implanted carrierelectrons is, from the view point of good balance ofelectro-conductivity and transparency, for example, in the range of from1×10¹⁸ /cm³ to 1×10²² /cm³ and replacing amount of each element can besuitably selected so that the compound has the amount of implantedelectrons in the range mentioned above. When the implanted amount ofelectrons is less than 1×10¹⁸ /cm³, sufficient electro-conductivitycannot be obtained. When it exceeds 1×10²² /cm³, absorption due toplasma oscillation appears in the visible region and thus transparencyis deteriorated. The amount of implanted carrier electrons is preferablyin the range of from 1×10¹⁹ /cm³ to 5×10²¹ /cm³.

Some of the elements used for the replacement may have properties ofabsorbing visible rays. Therefore, the amount of the replacing amount ofthe elements is suitably selected so that more than 70%, preferably morethan 80%, more preferably more than 90% of average visible lighttransmission can be obtained.

Specific examples of the oxides according to the second embodimentinclude electro-conductive oxide of the general formula: In₂ Ga₂ZnO_(7-d) wherein the oxygen deficit amount (d) is in the range of 0 to0.7, a part of at least one of In, Ga and Zn is replaced with otherelements, the elements replacing In and Ga are of trivalence or highervalence and the elements replacing Zn are of divalence or highervalence.

Indium and gallium are trivalent elements and so elements capable ofreplacing them are trivalent elements or elements of higher valence. Asthe valence of elements becomes higher, larger amount of carrierelectrons can be implanted with the same amount. While valence ofelements which can be used for the replacement is normally tri- tohexavalence, it is preferred to use elements of tetravalence or ofhigher valence as the replacing elements. Examples of the elements whichcan be used for the replacement are those mentioned hereinbefore.

Zn is a divalent element and so elements capable of replacing it aredivalent elements or elements of higher valence. As the valence ofelements becomes higher, larger amount of carrier electrons can beimplanted with the same amount. While valence of elements which can beused for the replacement is normally di- to hexavalence, it is preferredto use elements of trivalence or of higher valence as the replacingelements. Examples of the elements which can be used for the replacementare those mentioned hereinbefore.

The oxygen deficit amount (d) and the replaced amounts of In, Ga and Znelements are preferably selected so that the compounds has an amount ofcarrier electrons in the range of from 1×10¹⁸ /cm³ to 1×10²² /cm³.Preferred amount of carrier electrons is in the range of 1×10¹⁹ /cm³ to5×10²¹ /cm³.

Even though the oxygen deficit amount (d) is 0, oxides with a desiredelectro-conductivity can be obtained by suitably selecting the replacedamounts of the elements In, Ga and Zn. However, the oxygen deficitamount (d) exceeding 0.7 may cause absorption of visible light and henceis not preferred.

The oxygen deficit amount (d) is preferably in the range of 2.1×10⁻⁴ to0.7 from the viewpoint of endowing a preferred amount of carrierelectrons together with the replacing elements.

Specific examples of the oxides of the second embodiments include thoserepresented by the general formula: M(1)M(2)InO_(4-d), which correspondsto the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

where x, y and z are 1, where a part of M(1), M(2) and/or In is replacedwith one or more other elements. Examples of elements which can be usedfor the replacement are those described hereinbefore.

The electro-conductive oxides represented by the general formula:M(1)M(2)InO_(4-d) may also be represented by the general formula: Mg_(a)Zn₁.sbsb.-a Al_(b) Ga₁.sbsb.-b InO₄ wherein a is 0 to 1 and b is 0 to 1.That is, the oxides of the second embodiments include those representedby the general formula:

    Mg.sub.a Zn.sub.1.sbsb.-a Al.sub.b Ga.sub.1.sbsb.-b InO.sub.4

where a part of Mg, Zn, Al, Ga and In is replaced with one or more otherelements.

Examples of the above-mentioned oxides represented by Mg_(a) Zn₁.sbsb.-aAl_(b) Ga₁.sbsb.-b InO₄ include, for example, MgAlInO₄, ZnAlInO₄,MgGaInO₄, ZnGaInO₄, Mg_(a) An_(1-a) AlInO₄, Mg_(a) An_(1-a) GaInO₄,MaAl_(b) Ga₁.sbsb.-b InO₄ and ZnAl_(b) Ga₁.sbsb.-b InO₄. The values of aand b in the formulae may be suitably selected considering opticalproperties and electro-conductivity required for the electro-conductiveoxides depending on their compositions.

Due to the replacement of a part of at least one of M(1), M(2) and Inwith other elements, carrier electrons are implanted into the conductionbands. As described above, carrier electrons can be implanted intoconduction bands also by introducing oxygen deficit. Therefore, in theoxides of the second embodiment, carrier electrons are implanted intoconduction bands by replacement of elements, or by replacement ofelements and oxygen deficit.

The amount of carrier electrons is preferably in the range of from1×10¹⁸ /cm³ to 1×10²² /cm³ as described above. The amount of eachelement to be replaced, or the amounts of elements to be replaced andthe oxygen deficit amount are suitably selected so that the oxides havethe amount of carrier electrons in the range defined above. The amountof carrier electrons is preferably in the range of 1×10¹⁹ /cm³ to 5×10²¹/cm³.

Electro-conductive oxides according to the third embodiment of theinvention

As to the electro-conductive oxides according to the third embodiment ofthe invention, the descriptions hereinbefore for the electro-conductiveoxides according to the first embodiment of the invention about theirM(1), M(2), the ratio (x:y) and the ratio (z: y) in the general formula:

be applied. Further, in the electro-conductive oxides according to thethird embodiment of the invention, the oxides of the general formulamentioned above are implanted with cations.

In the electro-conductive oxides according to the third embodiment ofthe invention, other than the introduction of oxygen deficit,implantation of cation provides implantation of carrier electrons intoconduction bands and thereby electro-conductivity can be provided.

The cations implanted into the electro-conductive oxides according tothe third embodiment of the invention are not particularly limited solong as they can form solid solution with the oxides without destroyingcrystalline structures of the oxides. However, ions with a smaller ionicradius can more easily form solid solution by entering into crystallattice, whereas ions with a larger ionic radius are more likely todestroy crystalline structures.

Example of such cations are, for example, H, Li, Be, B, C, Na, Mg, Al,Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo,Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl,Pb and Bi.

Specific examples of the oxides of the third embodiment includeelectro-conductive oxides represented by the general formula: In₂ Ga₂ZnO_(7-d) wherein the oxygen deficit amount (d) is in the range of from0 to 0.7, which is implanted with cations.

Further specific examples of the oxide of the third embodiment areoxides of the general formula:

    M(1)M(2)InO.sub.4.sbsb.-4,

which corresponds to the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

where x, y are z are 1, which are implanted with cations.

The electro-conductive oxides of the general formula:M(1)M(2)InO₄.sbsb.-d may also be represented by the general formulaMg_(a) Zn₁.sbsb.-a Al_(b) Ga₁.sbsb.-b InO₄ where a is in a range of 0 to1 and b is in a range of 0 to 1. That is, the oxide of the thirdembodiment may be an oxide of the general formula: Mg_(a) Zn₁.sbsb.-aAl_(b) Ga₁.sbsb.-b InO₄ which is implanted with cations.

Examples of the above-mentioned oxides represented by Mg_(a) Zn₁.sbsb.-aAl_(b) Ga₁.sbsb.-b InO₄ include, as mentioned above, MgAlInO₄, AnAlInO₄,MgGaInO₄, ZnGaInO₄, Mg_(a) Zn₁.sbsb.-a AlInO₄, Mg_(a) Zn₁.sbsb.-aGaInO₄, MgAl_(b) Ga₁.sbsb.-b InO₄ and ZnAl_(b) Ga₁.sbsb.-b InO₄. Thevalues of a and b in the formulae may be suitably selected consideringoptical properties and electro-conductivity required for theelectro-conductive oxides depending on their compositions.

Electrodes of the invention

The electrode of the present invention is one consisting of antransparent substrate and an electro-conductive layer provided on atleast a part of at least one surface of the substrate, wherein theelectro-conductive layer comprises an electro-conductive oxide of anyone of the first, second and third embodiments of the present invention.

The electro-conductive layer of the electrode according to the presentinvention may be composed solely of the electro-conductive oxide of thefirst, second or third embodiment of the present invention, or it may bean oxide layer wherein those oxides coexist with other crystals.However, the amount of the coexisting other crystals should be selectedso that they do not cause any problems relating to transparency andelectro-conductivity of the oxide layer in practical use. Examples ofthe crystals which may coexist with the electro-conductive oxides of thepresent invention are, but not limited to, ITO, In₂ O₃ and SnO₂.

Preferably, the electrode of the present invention has aelectro-conductive layer on at least a part of at least one surface ofthe transparent substrate and the electro-conductive layer is composedsolely of the electro-conductive oxide and the faces (00n), where n is apositive integer, of the oxide are oriented in substantially parallelwith the surface of the transparent substrate, because such a structuremay produce higher electro-conductivity.

This point will be further explained by referring to the appendeddrawings.

The oxides of the present invention represented by the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)

basically have an octahedral structure composed of InO₆. FIG. 1 shows anatomic model of the octahedral structure of InO₆ where white circlesrepresent In atoms and black circles represent oxygen atoms. FIG. 1A isa view from a direction perpendicular to the faces (00n) and FIG. 1B isa view from a direction parallel with the faces (00n).

FIG. 2 is a schematic view of the relation of octahedrons of InO₆, faces(00n) of the octahedrons and the substrate.

In the electrode of the present invention, the faces (00n), where n is apositive integer, of the electro-conductive oxide are preferablyoriented in substantially parallel with the surface of the transparentsubstrate, because such a structure may produce higherelectro-conductivity. That is, as schematically shown in FIG. 3, routesfor electrons may be linear in oriented films and hence higherelectro-conductivity can be obtained, whereas the routes would be zigzagin non-oriented films.

The thickness of the electro-conductive layer of the electrode accordingto the invention may be suitably selected considering optical propertiesand conductivity required for the electrode, purpose of the electrodeand the like. For example, in the case of electrodes for liquid crystalpanels, it may be in a range of from about 30 nm to about 1 μm. Some ofthe elements contained in the oxide show absorbency in the visibleregion and, in such a case, a relatively thin film is preferred. Whenelements contained in the oxide show little or no absorbency in thevisible region, a larger thickness can be used and hence higherconductivity can be obtained.

The transparent substrate may be a transparent substrate made of glass,resins and the like.

Glass substrates are often used in liquid crystal displays and the like.Glass substrates may be composed either of soda lime glass or glass withlow alkalinity and, in general, soda lime glass is widely used. However,glass with low alkali content is suitable for color displays, highquality displays and the like. It is preferred to use glasses showinghigh transparency in the visible region and excellent in flatness.

Resin substrates may be, for example, polyester substrates, PMMAsubstrates or the like. Unlike glass substrates, resin substrates arerelatively light, thin and flexible, that is, they have more flexibilityin their shape. Therefore, there have been proposed various uses makingthe most of these properties of resin substrates. For example, they areused for films for electrophotography, liquid crystal displays, opticalmemories, transparent turbulent switches, antistatic films, heatreflecting films, planar heater films and the like. In the case ofliquid crystal displays, it is preferred to select substratesconsidering their processability, impact resistance, durability,adaptability to assembling process and the like, in addition to hightransparency in the visible region and good flatness.

The electrodes of the present invention may also have an underlyinglayer provided on the transparent substrate. Example of the underlyinglayer are color filters, TFT layers, EL luminescent layers, metallayers, semi-conductor layers, insulating layers and the like. Two ormore kinds of the underlying layers may be used simultaneously.

The electrodes of the present invention may be used for variousapplications. For example, they may be suitably used as electrodes ofliquid crystal displays, EL displays, solar cells and the like.

While liquid crystal displays are classified into various types such asTFT type, STN type and MIM type, all of them utilize the principle thata display is obtained by controlling the orientation direction of liquidcrystals retained between transparent electrodes by applying an electricfield to them. The electrodes of the present invention can be used assuch transparent electrodes.

For example, structure of color liquid crystal display of TFT typecomprises 6 parts, i.e., back lights, first polarizer, TFT substrate,liquid crystals, color filter substrate and second polarizer. It isnecessary to provide transparent electrodes on the TFT substrate and thecolor filter substrate to control the orientation direction of theliquid crystals. The transparent electrode of the present invention canbe formed on both of the TFT substrate and the color filter substrate bythe method described above. The transparent electrodes of the presentinvention are highly suitable for electrodes provided on TFT substratesor color filter substrates because they show high transparency andelectro-conductivity.

The transparent electrodes of the present invention may also be used aselectrodes for EL displays. EL displays are classified into varioustypes such as distributed type, Remosen type, double insulationstructure type and the like and all of them have a basic structure wherean EL luminescent layer is retained between a transparent electrode anda back electrode. The electrodes of the present invention areparticularly suitable for such a transparent electrode.

The electrodes of the present invention are also excellent as electrodesfor solar cells since they show high transparency andelectro-conductivity. While solar cells are classified into varioustypes such as pn junction type, Shottky barrier type, hetero junctiontype, hetero face junction type, pin type and the like, all of thesesolar cells have a basic structure where a semiconductor or an insulatoris retained between a transparent electrode and a back electrode. Sincesolar cells are elements for converting light energy into electricity byutilizing the photovoltaic effect at semi-conductor interfaces, it isrequired to lead light of spectrum as wide as possible to thesemi-conductor interface and hence transparency of the transparentelectrodes must be high. Further, since the transparent electrodes ofsolar cell have a function to collect photogenerated carriers generatedat the semi-conductor interface and lead them to terminals, thetransparent electrodes must have high electro-conductivity to collectthe photogenerated carriers as effectively as possible. Since thetransparent electrode of the present invention can lead light of a widespectrum covering all of the visible region including light of awavelength shorter than 450 nm to semi-conductor interfaces and,moreover, since they show high electro-conductivity, they are excellentas electrodes for solar cells.

Method for producing the electro-conductive oxides and the electrodes

The electro-conductive oxides of the first embodiment can be produced bypreparing an oxide in a conventional manner and introducing oxygendeficit into it. The preparation of the oxide itself can be carried outby a sintering technique, thin film technique or the like. When thepreparation of the oxide is carried out by a sintering technique or thelike, oxygen deficit may be introduced upon the formation of the oxidedepending on the process conditions.

The oxides can be produced in the sintering technique by weighing andmixing raw materials such as indium oxide, gallium oxide, magnesiumoxide, aluminium oxide and zinc oxide so that a resulting mixture has adesired composition, molding the mixture into a desired shape andsintering it at a temperature of from 1000° C. to 1700° C., for 1 to 48hours. When the temperature is below 1000° C. the reaction cannotproceed and hence the electro-conductive oxides of the present inventioncannot be obtained. When the temperature is above 1700° C., somematerials such as indium oxide and zinc oxide are vaporized and therebythe composition may be unacceptably changed.

The electrodes of the present invention can be manufactured by a thinfilm technique.

Representative examples of the thin film technique are, for example, CVDtechniques, injection spray control techniques, vacuum depositiontechniques, ion plating techniques, MBE techniques and sputteringtechniques. Examples of the CVD techniques include, for example, thermalCVD, plasma CVD, MOCVD and photo assisted CVD.

Chemical processes such as CVD techniques and injection spray controltechniques require simpler installations compared with physicalprocesses such as vacuum deposition techniques and sputtering techniquesand therefore suitable for the production of substrates of a large size.Further, since drying or sintering step for accelerating reactions orstabilizing physical properties requires a heat treatment at 350° to500° C., they are suitably used to produce oxides directly on glasssubstrates. However, they are not suitable for the case where oxides areformed on various underlying layers or on color filters and TFTelements.

Because the physical processes require a low temperature of 150° to 300°C. for the film formation, they are suitable for not only the directproduction on glass substrates but also the production on variousunderlying layers or on color filters and TFT elements. Among them,sputtering techniques are particularly preferred because, for example,they show high productivity and make possible to form a uniform filmeven on substrates of a large area.

Orientation properties of produced oxide films may vary depending on thetechnique used for the production of films and conditions used therein.

For example, in order to produce an oriented oxide thin film by asputtering technique, it is suitable to carry out the process by heatingtransparent substrates to a temperature of from 100° C. to 900° C. undera pressure of from 5×10⁻⁴ to 1 Torr.

As the sputtering target, sintering bodies of metals or oxides andmolded bodies of metal or oxide powders can be used.

In the case of oxides of the first embodiment, it is suitable to use asa target an oxide of the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)

wherein M(1) is at least one element selected from magnesium and zinc,M(2) is at least one element selected from aluminium and gallium, theratio (x:y) is from 0.1 to 2.2:1 and the ratio of (z:y) is 0.4 to 1.8:1.

By using the above-mentioned oxide as a target and carrying out the filmformation under the conditions of a substrate heating temperature offrom 100° to 900° C. and a pressure of from 5×10⁻⁴ to 1 Torr, it ispossible to produce on a transparent substrate an electro-conductivelayer comprising an oxide of the first embodiment of the presentinvention wherein faces (00n), where n is a positive integer, of theoxide are oriented in substantially parallel with the surface of thetransparent substrate.

In the CVD techniques, it is possible to use, as a source of metalelements, organic metals such as In(CH₃)₃, In(C₂ H₅)₃, In(C₅ H₇ O₂)₃,In(C₁₁ H₉ O₂)₃, Ga(CH₃)₃, Ga(C₂ H₅)₃, Zn(CH₃)₂, Zn(C₂ H₅)₂, Al(CH₃)₃,Al(C₂ H₅)₃, Mg(CH₃)₂ and Mg(C₂ H₅)₂, chlorides such as InCl₃, GaCl₃,ZnCl₂, AlCl₃, MgCl₂ and the like. As a source of oxygen, air, O₂, H₂ O,CO₂, N₂ O and the like can be used.

The film formation by ion plating techniques can be carried out byevaporating a mixture or a sintered body of raw materials of metals oroxides by ohmic-resistance heating, high frequency heating, electronimpact or the like and ionizing it by DC discharge, RF discharge,electron impact or the like. When metals are used as the raw materials,intended oxide films can be obtained by carrying out the film formationin a flow of air, O₂, H₂ O, CO₂, N₂ O or the like.

The film formation by vacuum deposition techniques can be carried out byevaporating a mixture or a sintered body of raw materials of metals oroxides by ohmic-resistance heating, high frequency heating, electronimpact, laser impact or the like under a pressure of 10⁻³ to 10⁻⁴ Torrto form a film on a substrate. When metals are used as the rawmaterials, intended oxide films can be obtained by carrying out the filmformation in a flow of air, H₂ O, CO₂, N₂ O or the like.

Also in CVD, ion plating and vacuum deposition techniques, orientedoxide films can be formed by suitably selecting the conditions of thefilm formation.

Electro-conductivity of the electro-conductive oxides of the firstembodiment of the present invention including the electro-conductivelayers of the electrodes can be obtained by introducing oxygen deficitinto the oxides represented by the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

obtained by a sintering technique or thin film technique. Generally,oxygen deficit of oxides can be realized by drawing oxygens out of theoxides. Oxygen atoms can be drawn out to obtain oxygen deficit by, forexample, heating the oxides in a reducing or inert gas atmosphere. Theheat and/or reducing treatment may be carried out at a temperature offrom 100° to 1100° C., preferably from 300° to 900° C.

Oxides with oxygen deficit can be also obtained by controlling oxygenpartial pressure during the sintering of oxides or the film formation.

The amount of oxygen deficit can be adjusted by introducing oxygendeficit upon formation of the oxides and then drawing out oxygens.

The electro-conductive oxides according to the second embodiment of thepresent invention are basically produced, like the electro-conductiveoxides of the first embodiment, by preparing an oxide in a conventionalmanner and, if necessary, introducing oxygen deficit into the obtainedoxide. The preparation of the oxide itself can be carried out by asintering technique, thin film technique or the like. When thepreparation of the oxide is carried out by a sintering technique or thelike, oxygen deficit may be introduced upon the formation of the oxidedepending on the process conditions. Examples of the thin film techniqueare those methods mentioned in the explanation about theelectro-conductive oxides of the first embodiment hereinbefore.

The oxides containing germanium as the replacing element can be producedin a sintering technique by weighing and mixing raw materials such asindium oxide, gallium oxide, zinc oxide and germanium oxide so that aresulting mixture has a composition, for example, In₂ Ga₂ Zn₀.99 Ge₀.01O₇, molding the mixture into a desired shape and sintering it at atemperature of, for example, from 1000° C. to 1700° C. for 1 to 48 hoursin air or inert gas atmosphere.

When the oxides are produced by a thin film technique, for example, asputtering technique, it is suitable to use, as a target, an oxiderepresented by the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3 y/.spsb.2.sub.+.spsb.3.sub.z.spsb./2)

wherein M(1) is at least one element selected from magnesium and zinc,M(2) is at least one element selected from aluminium and gallium, theratio (x:y) is within a range of 0.1 to 2.2:1 and the ratio (z:y) iswithin a range of 0.4 to 1.8:1, in which a part of at least one of M(1),M(2) and In is replaced with one or more other elements and the elementsreplacing M(1) are of di- or higher valence and the elements replacingM(2) and In are of tri- or higher valence.

For example, to form a layer having a composition of In₂ Ga₂ Zn₀.99Ge₀.01 O₇, a sintered body or a molded body of mixed powder having asimilar composition may be used as a target.

In order to produce an oriented oxide thin film by a sputteringtechnique, it is suitable to form an oxide film on a transparentsubstrate by using the above-described oxide as a target and heating thetransparent substrate to a temperature of from 100° C. to 900° C. undera pressure of from 5×10⁻⁴ to 1 Torr.

By the method described above, obtained is an electrode comprising anelectro-conductive layer comprising an electro-conductive oxide andhaving a crystalline structure where faces (00n), where n is a positiveinteger, of the electro-conductive oxide are oriented in substantiallyparallel with the surface of the transparent substrate.

Oxygen deficit can be introduced, like in the first embodiment of thepresent invention, for example, by drawing oxygen atoms out of oxide. Inaddition, when the electro-conductive oxides of the present inventionare produced by, for example, a sintering technique, they are likely toinherently have oxygen deficit. Obviously, the amount of oxygen deficitcan be adjusted by carrying out an additional step of drawing out oxygenatoms. Oxygen atoms can be drawn out to introduce oxygen deficit, forexample, by heating the oxides in a reducing or inert gas atmosphere.

The electro-conductive oxides according to the third embodiment of thepresent invention are produced, like the electro-conductive oxides ofthe first embodiment, basically by preparing an oxide having a desiredcomposition represented by the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.),

implanting cations into the obtained oxide and, optionally, introducingoxygen deficit into it. The preparation of the oxide itself can becarried out by a sintering technique, thin film technique or the like.When the preparation of the oxide is carried out by a sinteringtechnique, oxygen deficit may be introduced upon the formation of theoxide depending on the process conditions. Examples of the thin filmtechnique are those methods mentioned in the explanation about theelectro-conductive oxides of the first embodiment hereinabove.

An oxide represented by In₂ Ga₂ ZnO₇ and implanted with cations can beproduced, when the oxygen deficit amount (d) is 0, by producing an oxiderepresented by In₂ Ga₂ ZnO₇ in the same manner as in the production ofthe electro-conductive oxides of the first embodiment and implantingsuitable cations into it. Further, when the oxygen deficit amount (d)exceeds 0, such a compound can be produced by producing an oxiderepresented by In₂ Ga₂ ZnO_(7-d) in the same manner as used in thepreparation of the oxides of the first embodiment and implantingsuitable cations into it, or by producing an oxide represented by In₂Ga₂ ZnO₇, then implanting suitable cations into it and drawing oxygenatoms out of it.

The above-described procedure may be similarly used for the productionof electrodes comprising an electro-conductive layer ofelectro-conductive oxides according to the third embodiment.

Cations are implanted by an ion implantation technique. The ionimplantation technique may be the same as those used for introducingimpurity into solid materials in the manufacturing of VLSI and the like.Cation implantation can be achieved by ionizing elements correspondingto cations to be implanted, accelerating them to more than several tensof keV and implanting them into the oxide.

Implanted cations enter into crystal lattice to form a solid solutionand provide carrier electrons in conduction bands to showelectro-conductivity. When the oxides do not have oxygen deficit, theamount of implanted cations is preferably selected so that electrons inan amount of 1×10¹⁸ /cm³ to 1×10²² /cm³ are implanted into conductionbands. When the oxides have oxygen deficit, the amount of implantedcations is preferably selected so that the sum of the amounts of carrierelectrons generated by oxygen deficit and cation implantation fallswithin the range defined above.

When the amount of carrier electrons is less than 1×10¹⁸ /cm³,satisfactory electro-conductivity cannot be obtained. When it exceeds1×10²² /cm³, absorption in the visible region is caused by plasmaoscillation and transparency is deteriorated. The amount of carrierelectrons is preferably in a range of from 1×10¹⁹ /cm³ to 5×10²¹ /cm³.

EXAMPLES

The present invention will be further illustrated in detail by thefollowing working examples.

Example 1-1

Powders of In₂ O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), Ga₂O₃ (High Purity Chemicals Co. ,Ltd., 99.99% purity) and ZnO (High PurityChemicals Co. ,Ltd., 99.99% purity) were weighed and mixed so that theresulting mixture contained the metals in a ratio shown in Table 1. Theweighed powder mixture was charged in a polyamide container having 500ml volume, added with 200 g of zirconia beads having a diameter of 2 mm,and wet blended for 1 hour by means of an epicyclic ball mill (FritschJapan Co.,Ltd.). The dispersion medium was methanol. The mixed powderwas charged in an alumina crucible and calcined in air at 1000° C. for 5hours and again ground by using the epicyclic ball mill for 1 hour. Thusobtained calcined powder was molded by uniaxial compression (100 kg/cm²)into a disc sample having a diameter of 20 mm, which was sintered in airat 1400° C. for 2 hours to give a sintered body. This sintered body wasfurther heated to 880° C. for 2 hours in an argon atmosphere. Structureof the product was analyzed by an X-ray diffraction analyzer (MXP 18,Mac Science Co.,Ltd.) and it was confirmed that an oxide represented bythe formula: In₂ Ga₂ ZnO₇ had been produced.

In order to confirm electro-conductivity of the product, anelectro-conductive resin material K-1058 (Fujikura Kasei Co.,Ltd) wasapplied on four spots of the circumference of the disc sample and thesample was heated in an electric furnace maintained at 850° C. for 6minutes to form an electrode. Lead wires were soldered to thiselectrode, and electro-conductivity and amount of carrier electrons weredetermined by a van der Pauw technique electro-conductivity measuringapparatus.

To estimate light absorption properties of the product, the disc samplewas mounted on Model 330 spectrophotometer (Hitachi Electric Co.,Ltd.)and absorption was measured by the diffuse reflection method whilescanning from a wavelength of 500 nm to the shorter wavelength side. Awavelength at which the strength of the reflected light corresponds to50% of that of incident light was considered an absorption edgewavelength.

Oxygen deficit was obtained as follows. The sintered sample was ground,intimately mixed with carbon powder and placed in a quartz tube furnace.After evacuation to vacuum, Ar gas was flown into the furnace and it washeated to 600° C. Amount of carbon dioxide contained in the exhausted Argas was determined by infrared absorption spectrum analysis and theoxygen deficit was calculated from the amount.

Oxygen deficit, electro-conductivity, fundamental absorption edgewavelength and amount of carrier electrons determined as described aboveare shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                                             Amount of                                Atomic  Oxygen   Electro-   Absorption                                                                             carrier                                  ratio   deficit  conductivity                                                                             edge     electrons                                In  Ga    Zn    (d)    (S/cm)   (nm)     (/cm.sup.3)                          ______________________________________                                        2.0 2.0   1.0   5 × 10.sup.-3                                                                  1550     420      5 × 10.sup.20                  ______________________________________                                    

Examples 1-2 to 1-25

Powders of In₂ O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), Ga₂O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), ZnO (High PurityChemicals Co.,Ltd., 99.99% purity), SnO₂ (High Purity ChemicalsCo.,Ltd., 99.99% purity), SiO₂ (High Purity Chemicals Co.,Ltd., 99.99%purity), TiO₂ (High Purity Chemicals Co.,Ltd., 99.99% purity), V₂ O₅(High Purity Chemicals Co.,Ltd., 99.99% purity), GeO₂ (High PurityChemicals Co.,Ltd., 99.99% purity), ZrO₂ (High Purity ChemicalsCo.,Ltd., 99.99% purity), MoO₃ (High Purity Chemicals Co.,Ltd., 99.99%purity), Nb₂ O₅ (High Purity Chemicals Co.,Ltd., 99.99% purity) and Ta₂O₅ (High Purity Chemicals Co.,Ltd., 99.99% purity) were weighed andmixed so that the resulting mixtures contained the metals in the ratiosshown in Table 2 and disc samples were prepared in the same manner as inExample 1-1. Electro-conductivity, fundamental absorption edgewavelength and amount of carrier electrons of these samples are shown inTable 2.

                                      TABLE 2                                     __________________________________________________________________________                       Electro-    Amount of                                      Atomic ratio       condut-                                                                             Absorption                                                                          carrier                                           Replacing       ivity edge  electrons                                      Ex.                                                                              element                                                                              In Ga Zn (S/cm)                                                                              (nm)  (/cm.sup.3)                                    __________________________________________________________________________    1-2                                                                              Sn 0.002                                                                             1.998                                                                            2.000                                                                            1.000                                                                            1020  420   4 × 10.sup.20                            1-3                                                                              Sn 0.005                                                                             1.995                                                                            2.000                                                                            1.000                                                                            1210  420   5 × 10.sup.20                            1-4                                                                              Sn 0.010                                                                             1.990                                                                            2.000                                                                            1.000                                                                            1230  420   5 × 10.sup.20                            1-5                                                                              Sn 0.020                                                                             1.980                                                                            2.000                                                                            1.000                                                                            1110  420   5 × 10.sup.20                            1-6                                                                              Sn 0.040                                                                             1.960                                                                            2.000                                                                            1.000                                                                            1080  420   4 × 10.sup.20                            1-7                                                                              Ge 0.002                                                                             2.000                                                                            1.998                                                                            1.000                                                                            1040  420   4 × 10.sup.20                            1-8                                                                              Ge 0.005                                                                             2.000                                                                            1.995                                                                            1.000                                                                            1250  420   5 × 10.sup.20                            1-9                                                                              Ge 0.010                                                                             2.000                                                                            1.990                                                                            1.000                                                                            1360  420   5 × 10.sup.20                            1-10                                                                             Ge 0.020                                                                             2.000                                                                            1.980                                                                            1.000                                                                            1410  420   5 × 10.sup.20                            1-11                                                                             Ge 0.040                                                                             2.000                                                                            1.960                                                                            1.000                                                                            1500  420   5 × 10.sup.20                            1-12                                                                             Al 0.002                                                                             2.000                                                                            2.000                                                                            0.998                                                                            1120  420   4 × 10.sup.20                            1-13                                                                             Al 0.005                                                                             2.000                                                                            2.000                                                                            0.995                                                                            1210  420   4 × 10.sup.20                            1-14                                                                             Al 0.010                                                                             2.000                                                                            2.000                                                                            0.990                                                                            1280  420   4 × 10.sup.20                            1-15                                                                             Al 0.020                                                                             2.000                                                                            2.000                                                                            0.980                                                                            1270  420   4 × 10.sup.20                            1-16                                                                             Al 0.040                                                                             2.000                                                                            2.000                                                                            0.960                                                                            1150  420   4 × 10.sup.20                            1-17                                                                             Si 0.010                                                                             2.000                                                                            1.990                                                                            1.000                                                                            1080  420   4 × 10.sup.20                            1-18                                                                             Ti 0.010                                                                             2.000                                                                            1.990                                                                            1.000                                                                            1240  420   4 × 10.sup.20                            1-19                                                                             V 0.010                                                                              2.000                                                                            1.990                                                                            1.000                                                                            1150  420   4 × 10.sup.20                            1-20                                                                             Ge 0.010                                                                             2.000                                                                            1.990                                                                            1.000                                                                            1280  420   5 × 10.sup.20                            1-21                                                                             Zr 0.010                                                                             2.000                                                                            1.990                                                                            1.000                                                                            1110  420   4 × 10.sup.20                            1-22                                                                             V 0.010                                                                              2.000                                                                            2.000                                                                            0.090                                                                            1070  420   4 × 10.sup.20                            1-23                                                                             Mo 0.010                                                                             2.000                                                                            2.000                                                                            0.090                                                                            1090  420   4 × 10.sup.20                            1-24                                                                             Nb 0.010                                                                             2.000                                                                            2.000                                                                            0.090                                                                            1210  420   5 × 10.sup.20                            1-25                                                                             Ta 0.010                                                                             2.000                                                                            2.000                                                                            0.090                                                                            1180  420   5 × 10.sup.20                            __________________________________________________________________________

Example 1-26

A molded disc having a diameter of 25 mm was prepared from the calcinedpowder prepared in Example 1-1 by uniaxial compression (100 kg/cm²) andit was sintered in air at 1300° C. for 24 hours to yield a sinteredbody. The sintered body, of which surface had been polished, was fixedas a sputtering target on a backing plate with adhesive. This wasmounted on a Model BC1457 sputtering apparatus (ULVAC Japan Co.,Ltd.).An Ar/O₂ gas (Ar/O₂ ratio=40/10) was introduced into the apparatus andRF power of 180 W was inputted to form a thin film of a thickness ofabout 2000 Å on a quartz glass substrate heated to 500° C. This washeated to 400° to 1000° C. in air and then heated to 600° C. for 2 hoursunder an argon atmosphere.

Structure of the product was analyzed by the X-ray diffraction analyzerused in Example 1-1 and it was confirmed that the crystalline structureof In₂ Ga₂, ZnO₇ was produced. Oxygen deficit amount (d) was 5×10⁻²/cm².

Electro-conductivity and fundametal absorption edge wavelength of theproduct was determined in the same manner as in Example 1-1. However,since this sample was not a sintered body, the measurement offundamental absorption edge was carried out by the light transmissionmethod using the apparatus used in Example 1-1 and a wavelength at whichlight transmission began to decrease was considered fundamentalabsorption edge wavelength. Electro-conductivity, fundamental absorptionedge wavelength, transmission for 400 nm light and amount of carrierelectrons obtained as described above are shown in Table 3.

Example 1-27

A thin film was prepared in the same manner as described in Example1-26. However, since the thin film of this example was not subjected tothe heat treatment in an argon atmosphere, it did not showelectro-conductivity at that stage. H⁺ ions were implanted into thesample in an amount of 3×10¹⁶ ions/cm² at a doping rate of about 3μA/cm² and then structural analysis was carried out with the X-raydiffraction apparatus used in Example 1-26 to confirm that thecrystalline structure of In₂ Ga₂ ZnO₇ was maintained.Electro-conductivity, fundamental absorption edge wavelength,transmission for 400 nm light and amount of carrier electrons obtainedin the same manner as in Example 1-26 are shown in Table 3.

Comparative Example 1-1

Using an ITO target containing 5% Sn, an ITO thin film having athickness of about 2000 Å was formed on a quartz glass substrate in thesame manner as in Example 1-26. Electro-conductivity, fundamentalabsorption edge wavelength, transmission for 400 nm light and amount ofcarrier electrons of this ITO thin film were determined and are shown inTable 3.

Though the thin films of Examples 1-26 and 1-27 showedelectro-conductivity comparable to that of the thin film of ComparativeExample 1-1, they had the absorption edge wavelengths in the shorterwavelength region. Therefore, the thin films of Examples 1-26 and 1-27showed markedly higher transmission as to the light of 400 nm and itshowed substantially no coloration, whereas the thin film of ComparativeExample 1-1 clearly showed coloration in yellow.

                  TABLE 3                                                         ______________________________________                                                     Electro- Absorp-  Trans-                                                                              Amount of                                Atomic       condut-  tion     mission                                                                             carrier                                  ratio        ivity    edge     400 nm                                                                              electrons                                Example                                                                              In    Ga    Zn  (S/cm) (nm)   (%)   (/cm.sup.3)                        ______________________________________                                        1-26   2.0   2.0   1.0 1470   385    87    4 × 10.sup.20                1-27   2.0   2.0   1.0 1120   385    85    3 × 10.sup.20                1-1*   ITO (Sn 5 1240     405    42    5 × 10.sup.20                           mol %)                                                                 ______________________________________                                         *Comparative Example                                                     

Example 1-28

A thin film having a thickness of 2000 Å was prepared on a color filtersubstrate heated to 300° C. by using the sputtering target and thesputtering apparatus of Example 1-26, introducing an Ar/O₂ gas (Ar/O₂ratio=40/10) and inputting RF power of 100 W for 40 minutes. This washeated to 300° C. in air for 24 hours and structural analysis wascarried out with the X-ray diffraction apparatus used in Example 1-26 toconfirm that the crystalline structure of In₂ Ga₂ ZnO₇ was produced.

The product was further subjected to a heat treatment at 300° C. for 24hours to introduce oxygen deficit into it. Oxygen deficit amount (d) was2×10⁻² /cm².

Electro-conductivity, fundamental absorption edge wavelength,transmission (at 400 nm) and amount of carrier electrons were determinedin the same manner as in Example 1-26 and are shown in Table 4.

Comparative Example 1-2

Using an ITO target containing 5% Sn, an ITO thin film having athickness of about 2000 Å was formed on a color filter substrate in thesame manner as in Example 1-28. This was heated to 300° C. in air for 24hours and further subjected to a heat treatment at 300 ° C in an argonatmosphere for 24 hours. Electro-conductivity, fundamental absorptionedge wavelength, transmission for 400 nm light and amount of carrierelectrons of this ITO thin film were determined and are shown in Table4.

The thin film electrode of Example 1-28 showed electro-conductivitycomparable to that of the thin film of Comparative Example 1-2. However,the thin film electrode of Example 1-28 had the absorption edgewavelengths in the shorter wavelength region.

                  TABLE 4                                                         ______________________________________                                                     Electro- Absorp-  Trans-                                                                              Amount of                                Atomic       condut-  tion     mission                                                                             carrier                                  ratio        ivity    edge     400 nm                                                                              electrons                                Example                                                                              In    Ga    Zn  (S/cm) (nm)   (%)   (/cm.sup.3)                        ______________________________________                                        1-28   2.0   2.0   1.0 650    390    76    4 × 10.sup.20                1-2*   ITO (Sn 5 640      415    22    5 × 10.sup.20                           mol %)                                                                 ______________________________________                                         *Comparative Example                                                     

Examples 2-1 to 2-9

Powders of MgCO, (Kanto Chemical Co. ,Ltd., 42.7% purity in terms ofMgO), ZnO (High Purity Chemicals Co.,Ltd., 99.99% purity), Al₂ O₃ (HighPurity Chemicals Co.,Ltd., 99.99% purity), Ga₂ O₃ (High Purity ChemicalsCo.,Ltd., 99.99% purity) and In₂ O₃ (High Purity Chemicals Co.,Ltd.,99.99% purity) were weighed and mixed so that the resulting mixturescontained the metals in the ratios shown in Table 5. The weighed powdermixture was charged in a polyamide container having 500 ml volume with200 g of zirconia beads having a diameter of 2 mm, added with 20 g ofmethanol and wet blended for 1 hour by means of an epicyclic ball mill(Fritsch Japan Co. ,Ltd. ). The mixed powder was charged in an aluminacrucible and calcined in air at 1000° C. for 5 hours and again groundusing the epicyclic ball mill for 1 hour. Thus obtained calcined powderwas molded by uniaxial compression (100 kg/cm²) into disc samples havinga diameter of 20 mm, which were sintered in air at 1400° C. to 1700° C.for 2 hours to give sintered bodies having a relative density of morethan 90%.

Structures of the sintered bodies were analyzed by an X-ray diffractionapparatus (RADIIB, Rigaku Denki Co.,Ltd. ) and it was confirmed thatthey are single-phase samples composed solely of the crystallinestructure of YbFe₂ O₄ -type.

In order to implant electrons, the sintered bodies were wrapped to bemade into disc samples having a thickness of about 500 μm and subjectedto a reducing treatment in a hydrogen atmosphere at 600° C. to 800° C.Thus, the electro-conductive oxides of the present invention wereobtained.

In order to confirm electro-conductivity of the products, gold wasdeposited on the reduced disc samples at four spots on the circumferenceof each disc sample to make them electrodes. Lead wires were fixed tothe electrodes with silver paste and the other ends of the lead wirewere connected to a van der Pauw technique electro-conductivitymeasuring apparatus to determine electro-conductivity.

To estimate light absorption properties of the products, the discsamples having been subjected to the reducing treatment was mounted onModel 330 spectrophotometer (Hitachi Electric Co.,Ltd.) and absorptionwas measured by scanning from a wavelength of 500 nm to the shorterwavelength side. A wavelength at which the strength of the reflectedlight corresponds to 50% of that of incident light was considered anabsorption edge wavelength.

Electro-conductivity and absorption edge wavelength determined asdescribed above are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                        Ex-                            Electro-                                                                             Absorp-                                                                              Oxygen                           am-                            conduct-                                                                             tion   deficit                          ple  Mg     Zn    Alq  Ga  In  ivity  edge   amount                           ______________________________________                                        2-1  1.0    0.0   1.0  0.0 1.0 110 S/cm                                                                             330 nm 5 × 10.sup.-3              2-2  1.0    0.0   0.5  0.5 1.0  98    332    4 × 10.sup.-3              2-3  1.0    0.0   0.0  1.0 1.0 115    335    5 × 10.sup.-3              2-4  0.0    1.0   1.0  0.0 1.0 132    375    6 × 10.sup.-3              2-5  0.0    1.0   0.5  0.5 1.0 121    378    5 × 10.sup.-3              2-6  0.0    1.0   0.0  1.0 1.0 127    372    5 × 10.sup.-3              2-7  0.5    0.5   1.0  0.0 1.0 122    356    5 × 10.sup.-3              2-8  0.5    0.5   0.5  0.5 1.0 117    350    5 × 10.sup.-3              2-9  0.5    0.5   0.0  1.0 1.0 120    351    5 × 10.sup.-3              ______________________________________                                    

Examples 2-10 to 2-13

Powders of MgCO3 (Kanto Chemical Co.,Ltd., 42.7% purity in terms ofMgO), Ga₂ O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), In₂ O₃(High Purity Chemicals Co.,Ltd., 99.99% purity) and Al₂ O₃ (High PurityChemicals Co.,Ltd., 99.99% purity) were weighed and mixed so that theresulting mixtures contained the metals in the ratios shown in Table 6.Each of the weighed powder mixtures was charged in a polyamide containerhaving 500 ml volume with 200 g of zirconia beads having a diameter of 2mm, added with 20 g of methanol and wet blended for 1 hour by means ofan epicyclic ball mill (Fritsch Japan Co.,Ltd.). The mixed powder wascharged in an alumina crucible and calcined in air at 1000° C. for 5hours and again ground using the epicyclic ball mill for 1 hour. Thusobtained calcined powder was molded by uniaxial compression (100 kg/cm²)into disc samples having a diameter of 20 mm, which were sintered in anargon atmosphere at 1200° to 1700° C. for 2 hours to give sinteredbodies having a relative density of more than 90%.

Structures of the sintered bodies were analyzed in the same manner as inExample 2-1 and it was confirmed that they have the crystallinestructure of YbFe₂ O₄ -type. Then, the surfaces of the sintered bodieswere wrapped to made them into disc samples having a thickness of about500 μm. In order to evaluate electro-conductivity and absorption edge,electro-conductivity and light absorption properties were determined inthe same manner as in Example 2-1. The obtained electro-conductivitiesand absorption edge wavelengths are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                                       Electro-  Absorption                           Example                                                                              Mg      Al     Ga   In  conductivity                                                                            edge                                 ______________________________________                                        2-10   0.99    0.01   1.0  1.0 112 S/cm  331 nm                               2-11   0.97    0.03   1.0  1.0 122       332                                  2-12   0.95    0.05   1.0  1.0 124       330                                  2-13   0.93    0.07   1.0  1.0 121       331                                  ______________________________________                                    

Examples 2-14 to 2-21

Powders of ZnO (High Purity Chemicals Co.,Ltd., 99.99% purity) Ga₂ O₃(High Purity Chemicals Co.,Ltd., 99.99%), In₂ O₃ (High Purity ChemicalsCo.,Ltd., 99.99%), Al₂ O₃ (High Purity Chemicals Co.,Ltd., 99.99%), SiO₂(High Purity Chemicals Co.,Ltd., 99.99%), GeO₂ (Kanto Kagaku Co.,Ltd.,99.99%), SnO₂ (High Purity Chemicals Co.,Ltd., 99.99%) and Sb₂ O₃ (WakoJunyaku Kogyo Co.,Ltd., 95%) were weighed and mixed to replace 0.5% bymole of the cations of ZnGaInO₄, Zn, Ga or In so that the resultingmixtures have the compositions shown in Table 7.

The powders were mixed, calcined, molded and sintered in the same manneras in Examples of 2-10 to 2-13 to yield sintered bodies having arelative density of not less than 90% and it was confirmed that theyhave the crystalline structure of YbFe₂ O₄ -type. Then, the surfaces ofthe sintered bodies were wrapped to made them into disc samples having athickness of about 500 μm. In order to evaluate electro-conductivity andabsorption edge, electro-conductivity and light absorption propertieswere determined in the same manner as in Example 2-1. The obtainedelectro-conductivities and absorption edge wavelengths are shown inTable 7.

                  TABLE 7                                                         ______________________________________                                               Targeted        Electro-   Absorption                                  Example                                                                              Composition     conductivity                                                                             edge                                        ______________________________________                                        2-14   Zn.sub.0.995 Al.sub.0.006 GaInO.sub.4                                                         105 S/cm   370 nm                                      2-15   Zn.sub.0.995 Ga.sub.0.006 GaInO.sub.4                                                         125        375                                         2-16   Zn.sub.0.995 Si.sub.0.006 GaInO.sub.4                                                         132        372                                         2-17   Zn.sub.0.995 Ge.sub.0.006 GaInO.sub.4                                                         148        373                                         2-18   ZnGa.sub.0.995 Si.sub.0.005 InO.sub.4                                                         102        372                                         2-19   ZnGa.sub.0.995 Ge.sub.0.005 InO.sub.4                                                          90        370                                         2-20   ZnGaIn.sub.0.995 Sn.sub.0.005 O.sub.4                                                          75        375                                         2-21   ZnGaIn.sub.0.995 Sb.sub.0.005 O.sub.4                                                          84        377                                         ______________________________________                                    

Examples 2-22 to 2-30

Calcined powders were prepared in the same manner as in Example 2-1 sothat the resulting calcined powders contained metal elements in theratios shown in Table 8. The powders were molded into discs having adiameter of 25 mm by uniaxial compression (100 kg/cm²) and sintered inair at 1300° C. to 1700° C. for 2 hours to yield sintered bodies havinga relative density of not less than 90%. The surfaces of the sinteredbodies were polished and they were fixed on backing plates with adhesiveas sputtering targets. They were mounted on a Model BC1457 sputteringapparatus (Nippon Shinku Co.,Ltd.). An Ar/O₂ gas (Ar/O₂ ratio=45/5) wasintroduced into the apparatus and RF power of 180 W was inputted for 40minutes to form thin amorphous films of a thickness of about 800 Å on aquartz glass substrate heated to 500° C. They were heated to 400° to800° C. in air. Structural analysis of the products was carried out withthe apparatus used in Example 2-1 to confirm that crystals with theYbFe₂ O₄ -type structure had been produced.

Then, in order to implant electrons, the crystallized thin film sampleswere treated in a hydrogen flow at 400° C. to 800° C. to yield theelectro-conductive oxides of the present invention. Electro-conductivityand absorption edge wavelength of these electro-conductive oxides weredetermined in the same manner as in Example 2-1. Absorption edgewavelength was determined by the light transmission method and awavelength at which the transmission was 50% was considered theabsorption edge wavelength. The obtained electro-conductivities andabsorption edge wavelengths are shown in Table 8. The results shown inTable 8 clearly demonstrate that the electro-conductive oxides areexcellent as electrodes.

                  TABLE 8                                                         ______________________________________                                                                          Electro- Absorption                         Example                                                                              Mg     Zn     Al  Ga  In   Conductivity                                                                           edge                               ______________________________________                                        2-22   1.0    0.0    1.0 0.0 1.0  90 S/cm  335 nm                             2-23   1.0    0.0    0.5 0.5 1.0  91       337                                2-24   1.0    0.0    0.0 1.0 1.0  90       330                                2-25   0.0    1.0    1.0 0.0 1.0  92       371                                2-26   0.0    1.0    0.5 0.5 1.0  88       375                                2-27   0.0    1.0    0.0 1.0 1.0  73       379                                2-28   0.5    0.5    1.0 0.0 1.0  92       350                                2-29   0.5    0.5    0.5 0.5 1.0  84       352                                2-30   0.5    0.5    0.0 1.0 1.0  90       355                                ______________________________________                                    

Examples 3-1 to 3-9

Powders of In₂ O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), Ga₂O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity) and ZnO (High PurityChemicals Co.,Ltd., 99.99% purity) were weighed and mixed so that theresulting mixtures contained the metals in the ratios shown in Table 9.The weighed powder mixtures were charged in a polyamide container having500 ml volume, added with 200 g of zirconia beads having a diameter of 2mm and wet blended for 1 hour by means of an epicyclic ball mill(Fritsch Japan Co.,Ltd. ). The dispersion medium was methanol. The mixedpowders were charged in an alumina crucible and calcined in air at 1000°C. for 5 hours and again ground for 1 hour using the epicyclic ballmill. Thus obtained calcined powders were molded by uniaxial compression(100 kg/cm²) into discs having a diameter of 20 mm, which were sinteredin air at 1400° C. for 2 hours to give sintered bodies. These sinteredbody were further heated to 880° C. for 2 hours in an argon atmosphere.

Measurements and calculations of of electro-conductivity, absorptionedge wavelength and oxygen deficit amount were carried out in the samemanner as in Example 1-1. The obtained electro-conductivities,absorption edge wavelengths and oxygen deficit amounts are shown inTable 9.

                                      TABLE 9                                     __________________________________________________________________________                    Electro-                                                                           Absorp-    Amount of                                                     conduc-                                                                            tion Oxygen                                                                              carrier                                       Exam-                                                                             Atomic ratio                                                                              tivity                                                                             edge deficit                                                                             electrons                                     ple Zn                                                                              Ga                                                                              In                                                                              x/y                                                                              z/y                                                                              (S/cm)                                                                             (nm) d     (/cm.sup.3 g)                                 __________________________________________________________________________    3-1 11                                                                              47                                                                              41                                                                              0.24                                                                             0.87                                                                             980  390  5 × 10.sup.-3                                                                 3 × 10.sup.20                           3-2 25                                                                              39                                                                              36                                                                              0.64                                                                             0.92                                                                             1420 420  5 × 10.sup.-3                                                                 5 × 10.sup.20                           3-3 33                                                                              34                                                                              33                                                                              0.97                                                                             0.97                                                                             2520 420  5 × 10.sup.-3                                                                 5 × 10.sup.20                           3-4 47                                                                              39                                                                              24                                                                              1.63                                                                             0.82                                                                             870  430  5 × 10.sup.-3                                                                 3 × 10.sup.20                           3-5 11                                                                              38                                                                              52                                                                              0.28                                                                             1.38                                                                             1170 400  5 × 10.sup.-3                                                                 4 × 10.sup.20                           3-6 40                                                                              27                                                                              34                                                                              1.50                                                                             1.27                                                                             820  430  4 × 10.sup.-3                                                                 3 × 10.sup.20                           3-7  7                                                                              28                                                                              65                                                                              0.25                                                                             2.33                                                                             970  400  4 × 10.sup.-3                                                                 3 × 10.sup.20                           3-8 34                                                                              44                                                                              22                                                                              0.78                                                                             0.50                                                                             950  420  4 × 10.sup.-3                                                                 3 × 10.sup.20                           3-9 16                                                                              27                                                                              57                                                                              0.61                                                                             2.13                                                                             780  430  3 × 10.sup.-3                                                                 2 × 10.sup.20                           __________________________________________________________________________

Comparative Examples 3-1 to 3-4

Example 3-1 was repeated except that the powders were mixed so that theresulting mixed powder contained the metals in the ratios shown in Table10. Results are shown in Table 10.

                                      TABLE 10                                    __________________________________________________________________________                    Electro-                                                                           Absorp-    Amount of                                                     conduc-                                                                            tion Oxygen                                                                              carrier                                       Exam-                                                                             Atomic ratio                                                                              tivity                                                                             edge deficit                                                                             electrons                                     ple Zn                                                                              Ga                                                                              In                                                                              x/y                                                                              z/y                                                                              (S/cm)                                                                             (nm) d     (/cm.sup.3 g)                                 __________________________________________________________________________    3-1  6                                                                              36                                                                              58                                                                              0.17                                                                             1.61                                                                             210  390  1 × 10.sup.-3                                                                 5 × 10.sup.19                           3-2 44                                                                              16                                                                              40                                                                              2.75                                                                             2.50                                                                             720  460  3 × 10.sup.-3                                                                 2 × 10.sup.20                           3-3 12                                                                              72                                                                              16                                                                              0.17                                                                             0.22                                                                             70   370  5 × 10.sup.-3                                                                 1 × 10.sup.19                           3-4 62                                                                              30                                                                               8                                                                              2.07                                                                             0.27                                                                             560  430  4 × 10.sup.-3                                                                 2 × 10.sup.20                           __________________________________________________________________________

Examples 3-10 to 3-14

Powders of In₂ O₃, (High Purity Chemicals Co.,Ltd., 99.99% purity), Ga₂O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), ZnO (High PurityChemicals Co.,Ltd., 99.99% purity), MgCO₃ (Kanto Kagaku Co.,Ltd., 99.99%purity) and Al₂ O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity) wereweighed and mixed so that the resulting mixed powders contained themetals in the ratios shown in Table 11 and the powders were treated inthe same manner as in Example 3-1. Results are shown in Table 11.

                                      TABLE 11                                    __________________________________________________________________________                         Electro-                                                                           Absorp-   Amount of                                                      conduc-                                                                            tion Oxygen                                                                             carrier                                   Exam-                                                                             Atomic ratio     tivity                                                                             edge deficit                                                                            electrons                                 ple Zn                                                                              Mg Ga                                                                              Al                                                                              In                                                                              x/y                                                                              z/y                                                                              (S/cm)                                                                             (nm) × 10.sup.-3                                                                  (/cm.sup.3 g)                             __________________________________________________________________________    3-10                                                                              25     39                                                                              36                                                                              0.24                                                                             0.87                                                                             1360 420  5    5 × 10.sup.20                       3-11  25 39  36                                                                              0.24                                                                             0.87                                                                             920  340  4    3 × 10.sup.20                       3-12  25   39                                                                              36                                                                              0.24                                                                             0.87                                                                             910  340  4    3 × 10.sup.20                       3-13                                                                              26                                                                               7 33  34                                                                              1.00                                                                             1.03                                                                             1280 390  5    5 × 10.sup.20                       3-14                                                                              33   28                                                                               6                                                                              33                                                                              0.97                                                                             0.97                                                                             1360 420  5    5 × 10.sup.20                       __________________________________________________________________________

Example 3-15 to 3-24

Powders of In₂ O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), Ga₂O₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), ZnO (High PurityChemicals Co.,Ltd., 99.99% purity), Al₂ O₃ (High Purity ChemicalsCo.,Ltd., 99.99% purity), SnO₂ (High Purity Chemicals Co.,Ltd., 99.99%purity), SiO₂ (High Purity Chemicals Co.,Ltd., 99.99% purity), TiO₂(High Purity Chemicals Co.,Ltd., 99.99% purity), V₂ O₅ (High PurityChemicals Co.,Ltd., 99.99% purity), GeO₂ (High Purity ChemicalsCo.,Ltd., 99.99% purity), ZrO₂ (High Purity Chemicals Co.,Ltd., 99.99%purity), MoO₃ (High Purity Chemicals Co.,Ltd., 99.99% purity), Nb₂ O₅(High Purity Chemicals Co.,Ltd., 99.99% purity) and Ta₂ O₅ (High PurityChemicals Co.,Ltd., 99.99% purity) were weighed and mixed so that theresulting mixed powders contained the metals in the ratios shown inTable 12 and the powders were treated in the same manner as in Example3-1 to prepare disc samples. Electro-conductivities, fundamentalabsorption edge wavelengths and amounts of carrier electrons of thesesamples are shown in Table 12.

                                      TABLE 12                                    __________________________________________________________________________                        Electro-                                                                           Absorp-                                                                            Amount of                                                           conduc-                                                                            tion carrier                                         Exam-                                                                             Atomic ratio    tivity                                                                             edge electrons                                       ple Zn                                                                              Ga                                                                              In                                                                              Other                                                                             x/y                                                                              z/y                                                                              (S/cm)                                                                             (nm) (/cm.sup.3 g)                                   __________________________________________________________________________    3-15                                                                              24                                                                              39                                                                              36                                                                              Sn 1                                                                              0.64                                                                             0.92                                                                             1580 420  6 × 10.sup.20                             3-16                                                                              24                                                                              39                                                                              36                                                                              Ge 1                                                                              0.64                                                                             0.92                                                                             1620 420  6 × 10.sup.20                             3-17                                                                              24                                                                              39                                                                              36                                                                              Al 1                                                                              0.64                                                                             0.92                                                                             1510 420  6 × 10.sup.20                             3-18                                                                              24                                                                              39                                                                              36                                                                              Si 1                                                                              0.64                                                                             0.92                                                                             1380 420  6 × 10.sup.20                             3-19                                                                              24                                                                              39                                                                              36                                                                              Ti 1                                                                              0.64                                                                             0.92                                                                             1240 420  5 × 10.sup.20                             3-20                                                                              24                                                                              39                                                                              36                                                                              V 1 0.64                                                                             0.92                                                                             1680 420  6 × 10.sup.20                             3-21                                                                              24                                                                              39                                                                              36                                                                              Zr 1                                                                              0.64                                                                             0.92                                                                             1590 420  6 × 10.sup.20                             3-22                                                                              24                                                                              39                                                                              36                                                                              Mo 1                                                                              0.64                                                                             0.92                                                                             1630 420  6 × 10.sup.20                             3-23                                                                              24                                                                              39                                                                              36                                                                              Nb 1                                                                              0.64                                                                             0.92                                                                             1540 420  6 × 10.sup.20                             3-24                                                                              24                                                                              39                                                                              36                                                                              Ta 1                                                                              0.64                                                                             0.92                                                                             1430 420  6 × 10.sup.20                             __________________________________________________________________________

Example 3-25

The calcined powder obtained in Example 3-1 was molded into a dischaving a diameter of 25 mm by uniaxial compression (100 kg/cm²) andsintered in air at 1300° C. for 24 hours to yield a sintered body. Thesurface of the sintered body was polished and it was fixed on a backingplate with adhesive as a sputtering target. It was mounted on a ModelBC1457 sputtering apparatus (Nippon Shinku Co.,Ltd.). An Ar/O₂ gas(Ar/O₂ ratio=40/10) was introduced into the apparatus and RF power of180 W was inputted for 40 minutes to form a thin film of a thickness ofabout 2000 Å on a quartz glass substrate heated to 500° C.

It was heated to 400° to 1000° C. in air and further heated to 880° C.for 2 hours in an argon atmosphere.

Since this sample was not a sintered body, the measurement of absorptionedge was carried out by the light transmission method using theapparatus used in Example 3-1 and a wavelength at which lighttransmission began to decrease was considered absorption edgewavelength. Electro-conductivity, fundamental absorption edgewavelength, transmission for 400 nm light and amount of carrierelectrons obtained as described above are shown in Table 13.

Example 3-26

A thin film was prepared in the same manner as described in Example3-25. However, since the thin film of this example was not subjected tothe heat treatment in an argon atmosphere, it did not showelectro-conductivity at that stage. H⁺ ions were implanted into thesample in an amount of 3×10¹⁶ ions/cm² at a doping rate of about 3μA/cm² and then composition was analyzed by an X-ray diffractionapparatus to confirm that the composition of Zn₀.24 GaIn₀.87 O₂.55 wasmaintained. Electro-conductivity, absorption edge, transmission for 400nm light and amount of carrier electrons obtained in the same manner asin Example 3-25 are shown in Table 13.

Example 3-27

A thin film having a thickness of 2000 Å was prepared on a color filtersubstrate heated to 300° C. by using the sputtering target and thesputtering apparatus of Example 3-25, introducing an Ar/O₂ gas (Ar/O₂ratio=40/10) and inputting RF power of 100 W for 40 minutes. This washeated to 300° C. in air for 24 hours and composition analysis wascarried out with an X-ray diffraction apparatus to confirm that thecomposition of Zn₀.24 GaIn₀.87 O₂.55 had been produced.

The product was further subjected to a heat treatment at 300° C. for 24hours in an argon atmosphere to introduce oxygen deficit into it. Oxygendeficit amount (d) was 2×10⁻² /cm³.

Electro-conductivity, fundamental absorption edge wavelength,transmission (at 400 nm) and amount of carrier electrons were determinedin the same manner as in Example 3-25 and are shown in Table 13.

                                      TABLE 13                                    __________________________________________________________________________                    Electro-                                                                           Absorp-                                                                            Trans-                                                                             Amount of                                                      conduc-                                                                            tion mission                                                                            carrier                                        Exam-                                                                             Atomic ratio                                                                              tivity                                                                             edge 400 nm                                                                             electrons                                      ple Zn                                                                              Ga                                                                              In                                                                              x/y                                                                              z/y                                                                              (S/cm)                                                                             (nm) (%)  (/cm.sup.3 g)                                  __________________________________________________________________________    3-25                                                                              25                                                                              39                                                                              36                                                                              0.64                                                                             0.92                                                                             1210 385  91   5 × 10.sup.20                            3-26                                                                              25                                                                              39                                                                              36                                                                              0.64                                                                             0.92                                                                             1380 380  94   6 × 10.sup.20                            3-27                                                                              25                                                                              39                                                                              36                                                                              0.64                                                                             0.92                                                                             680  390  74   3 × 10.sup.20                            __________________________________________________________________________

Example 4-1

A thin film having a thickness of 2000 Å was prepared on a quartz glasssubstrate by an RF magnetron sputter using a sintered body having acomposition of ZnO/Ga₂ O₃ /In₂ O₃ =16/43/41 as a sputtering target underthe following conditions: Ar/O₂ ratio=18/2, pressure=6×10⁻³ Torr andsubstrate heating temperature=500° C. Composition of the obtained thinfilm was analyzed with fluorescent X-ray (XRF) and it was found that thefilm had a composition of Zn/Ga/In=11/47/41 (x/y=0.24, z/y=0.87).Further, when crystallinity was examined by XRD, a diffraction peak wasobserved only for faces (009) and thus the film was confirmed to have anoriented structure. Electro-conductivity measured by the four probemethod was 280 S/cm and absorption edge obtained by measuringtransmission was 390 nm.

Example 4-2

A thin film having a thickness of 2000 Å was prepared on a quartz glasssubstrate by an RF magnetron sputter using a sintered body having acomposition of ZnGaInO₄ as a sputtering target under the followingconditions: Ar/O₂ ratio=18/2, pressure=1×10⁻² Torr and substrate heatingtemperature=500° C. Composition of the obtained thin film was analyzedwith fluorescent X-ray (XRF) and it was found that the film had acomposition of Zn/Ga /In=25/39/36 (x/y=0.64, z/y=0.92). Further, whencrystallinity was examined by XRD, a diffraction peak was observed onlyfor faces (009) and thus the film was confirmed to have an orientedstructure. Electro-conductivity measured by the four probe method was240 S/cm and absorption edge obtained by measuring transmission was 385nm.

Example 4-3

The thin film obtained in Example 4-2 was subjected to a 98/2). As aresult, electro-conductivity of 1370 S/cm was obtained.

Example 4-4

A thin film having a thickness of 1500 Å was prepared on a quartz glasssubstrate by an RF magnetron sputter using a sintered body having acomposition of ZnO/Ga₂ /O₃ /In₂ O₃ =40/29/31 as a sputtering targetunder the following conditions: Ar/O₂ ratio=18/2, pressure=1×10⁻² Torrand substrate heating temperature=500° C. Composition of the obtainedthin film was analyzed with fluorescent X-ray (XRF) and it was foundthat the film had a composition of Zn/Ga/In=33/34/33 (x/y=0.97, z/y=0.97). Further, when crystallinity was examined by XRD, a diffractionpeak was observed only for faces (009) and thus the film was confirmedto have an oriented structure. Electro-conductivity measured by the fourprobe method was 620 S/cm and absorption edge obtained by measuringtransmission was 380 nm. Example 4-5

A thin film having a thickness of 1500 Å was prepared on a quartz glasssubstrate by an RF magnetron sputter using a sintered body having acomposition of ZnO/Ga₂ O₂ O₃ /In₂ O₃ =45/25/35 as a sputtering targetunder the following conditions: Ar/O₂ ratio=19.5/0.5, pressure=8×10⁻³Torr and substrate heating temperature=400° C. The obtained thin filmwas subjected to a heat treatment in air at 600° C. for 1 hour and thento a reducing treatment in N₂ /H₂ gas flow (N₂ /H₂ =98/2) at 500° C. for1 hour. Electro-conductivity measured by the four probe method was 1270S/cm and absorption edge obtained by measuring transmission was 380 nm.

Composition of the obtained thin film was analyzed with fluorescentX-ray (XRF) and it was found that the film had a composition ofZn/Ga/In=39/28/33 (x/y=1.37, z/y=1.17). Further, when crystallinity wasexamined by XRD, a diffraction peak was observed only for faces (009)and thus the film was confirmed to have an oriented structure.

The results of Examples 4-1 to 4-5 are summarized in Table 14.

                  TABLE 14                                                        ______________________________________                                                                         Electro-  Absorption                                                          conductivity                                                                            edge                               Example                                                                              Zn    Ga    In  x/y  z/y  (S/cm)    (nm)                               ______________________________________                                        4-1    11    47    41  0.24 0.87 280       390                                4-2    25    39    36  0.64 0.92 240       385                                4-3    25    39    36  0.64 0.92 1370      380                                4-4    33    34    33  0.97 0.97 620       380                                4-5    39    28    33  1.37 1.17 1270      380                                ______________________________________                                    

Example 4-6

A thin film having a thickness of 5000 Å was prepared on a quartz glasssubstrate by an RF magnetron sputter using a sintered body having acomposition of ZnO/MgO/Ga₂ O₃ /In₂ O₃ =30/6/30/34 as a sputtering targetunder the following conditions: Ar/O₂ ratio=18/2, pressure=5×10⁻¹ Torrand substrate heating temperature=500° C. Composition of the obtainedthin film was analyzed with fluorescent X-ray (XRF) and it was foundthat the film had a composition of Zn/Mg/Ga/In=26/7/33/34 (x/y=1.00,z/y=1.03). Further, when crystallinity was examined by XRD, diffractionpeaks were observed only for faces (003), (006) and (009) and thus thefilm was confirmed to have an oriented structure.

The obtained thin film was subjected to a reducing treatment in N_(2/)H₂ gas flow (N₂ /H₂ =98/2) at 600° C for 1 hour. Electro-conductivitymeasured by the four probe method was 1070 S/cm and absorption edgeobtained by measuring transmission was 360 nm.

Example 4-7

A thin film having a thickness of 5000 Å was prepared on a quartz glasssubstrate by an RF magnetron sputter using a sintered body having acomposition of ZnO/Ga₂ O₃ /Al₂ O₃ /In₂ O₃ =37/25/5/33 as a sputteringtarget under the following conditions: Ar/O₂ ratio=18/2, pressure=10mTorr and substrate heating temperature=500° C.

Composition of the obtained thin film was analyzed with fluorescentX-ray (XRF) and it was found that the film had a composition ofZn/Ga/Al/In=33/28/6/33 (x/y=0.97, z/y=0.97). Further, when crystallinitywas examined by XRD, diffraction peaks were observed only for faces(003), (006) and (009) and thus the film was confirmed to have anoriented structure.

The obtained thin film was subjected to a reducing treatment in N₂ /H₂gas flow (N₂ /H₂ =98/2) at 600° C. for 1 hour. Electro-conductivitymeasured by the four probe method was 1080 S/cm and absorption edgeobtained by measuring transmission was 355 nm.

The results of Examples 4-6 and 4-7 are summarized in Table 15.

                  TABLE 15                                                        ______________________________________                                                                                Electro-                              Ex-                                     conduc-                                                                              Absorption                     am-                                     tivity edge                           ple  Zn    Mg     Ga  Al  In  x/y  z/y  (S/cm) (nm)                           ______________________________________                                        4-6  26    7      33  0   34  1.00 1.03 1070   360                            4-7  33    0      28  6   33  0.97 0.97 1080   355                            ______________________________________                                    

Examples 4-8 to 4-12

A thin film having a thickness of 2000 Å was prepared on a quartz glasssubstrate by an RF magnetron sputter using a sintered body having acomposition of ZnO/Ga₂ O₃ /In₂ O₃ =40/29/31 added with SnO₂, GEO₂, SiO₂,TiO₂ or V₂ O₅ as a sputtering target under the following conditions:Ar/O₂ ratio=19.5/0.5, pressure=10 mTorr and substrate heatingtemperature=500° C. Composition of the obtained thin film was analyzedwith fluorescent x-ray (XRF) and it was found that the film had acomposition of Zn/Ga/In=33/34/33 (x/y=0.97, z/y=0.97) and contained 1%of Sn, Ge, Si, Ti or V. Further, when crystallinity was examined by XRD,a diffraction peak was observed only for faces (009) and thus the filmwas confirmed to have an oriented structure. Electro-conductivitymeasured by the four probe method and absorption edge were shown inTable 16.

                  TABLE 16                                                        ______________________________________                                                                  Electro-                                                                      conduc-  Absorption                                 Exam- Atomic ratio        yivity   edge                                       ple   Zn    Ga    In  Other x/y  z/y  (S/cm) (nm)                             ______________________________________                                        4-8   32    34    33  Sn 1  0.94 0.97 1080   385                              4-9   32    34    33  Ge 1  0.94 0.97  960   390                              4-10  32    34    33  Si 1  0.94 0.97  930   380                              4-11  32    34    33  Ti 1  0.94 0.97 1080   385                              4-12  32    34    33  V 1   0.94 0.97 1020   390                              ______________________________________                                    

Example 4-13

Production of electrodes by plasma CVD

A quartz glass substrate was placed in a chamber, starting materials,In(CH₃)₃, Ga(CH₃)₃ and Zn(C₂ H₅)₂, were introduced into the chamber withan Ar carrier gas, and N₂ O gas were also introduced into the chamber. Athin film obtained under the conditions of a substrate heatingtemperature of 500° and a pressure of 1 Torr had a composition ofZn/Ga/Al=29/36/35 (x/y=0.81, z/y=0.97) analyzed with fluorescent x-ray(XRF). When crystallinity was examined by XRD, diffraction peaks wereobserved only for faces (003), (006) and (009) and thus the film wasconfirmed to have an oriented structure.

The obtained thin film was subjected to a reduction heat treatment in N₂/H₂ gas flow (N₂ /H₂ =98/2) at 400° C. for 30 minutes.Electro-conductivity measured by the four probe method was as high as1310 S/cm and absorption edge obtained by measuring transmission was 355nm.

Example 4-14

Production of electrodes by ion plating

A thin film was prepared on a quartz glass substrate by bombarding withan electron beam a sintered body having a composition of ZnO/Ga₂ O₃ /In₂O₃ =40/29/31 to vaporize it and ionizing in by RF discharge between thetarget and the substrate. The obtained thin film had a composition ofZn/Ga/In=33/38/29 (x/y =0.89, z/y=0.76) analyzed with fluorescent X-ray(XRF). When crystallinity was examined by XRD, a diffraction peak wasobserved only for faces (009) and thus the film was confirmed to have anoriented structure. The thin film was subjected to a reduction heattreatment in N₂ /H₂ gas flow (N₂ /H₂ =98/2) at 500° C. for 30 minutes.Electro-conductivity measured by the four probe method was 1110 S/cm andabsorption edge obtained by measuring transmission was 380 nm.

Example 4-15

A thin film was prepared on a quartz glass substrate by the electronbeam deposition technique using a sintered body having a composition ofZnO/Ga₂ O₃ /In₂ O₃ =40/29/31 as a target under the condition ofsubstrate heating temperature of 500° C. The obtained thin film had acomposition of Zn/Ga/In=31/40/29 (x/y=0.78, z/y=0.73) analyzed withfluorescent X-ray (XRF). When crystallinity was examined by XRD, adiffraction peak was observed only for faces (009) and thus the film wasconfirmed to have an oriented structure.

The thin film was subjected to a reduction heat treatment in N₂ /H₂ gasflow (N₂ =98/2) at 500° C. for 30 minutes. Electro-conductivity measuredby the four probe method was 1010 S/cm and absorption edge obtained bymeasuring transmission was 380 nm.

Example 4-16

A thin film was prepared on a quartz glass substrate by an RF magnetronsputter using a sintered body having a composition of ZnO/Ga₂ O₃ /In₂ O₃=40/29/31 as a sputtering target under the following conditions: Ar/O₂ratio=18/2, pressure=1×10⁻³ Torr and substrate heating temperature=500°C. Composition of the obtained thin film was analyzed with fluorescentX-ray (XRF) and it was found that the film had a composition ofZn/Ga/In=33/34/33 (x/y=0.97, z/y=0.97). When crystallinity was examinedby XRD, a diffraction peak was observed only for faces (009) and thusthe film was confirmed to have an oriented structure.

This thin film was implanted with H⁺ ions at an accelerating voltage of80 keV to an amount of 2×10¹⁶ ions/cm². Electro-conductivity measured bythe four probe method was 1320 S/cm and absorption edge obtained bymeasuring transmission was 370 nm.

According to the present invention, there can be provided novelelectro-conductive oxides, which have an absorption edge at a wavelengthshorter than 450 nm and electro-conductivity comparable to or higherthan that of ITO, and do not cause coloration when they have a thicknesslarger than that of ITO thin films.

According to the present invention, there can be further providedelectrodes useful for liquid crystal displays, EL displays, solar cellsand the like by using the above-described electro-conductive oxides. Inparticular, the electrodes comprising the electro-conductive oxides ofthe present invention show higher electro-conductivity since the faces(00n), where n is an positive integer, of the electro-conductive oxidesare oriented in substantially parallel with the surface of a transparentsubstrate.

What is claimed is:
 1. An electro-conductive oxide represented by thegeneral formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is at least one element selected from the group consistingof magnesium and zinc, M(2) is at least one element selected from thegroup consisting of aluminium and gallium, the ratio (x:y) is within arange of 0.2 to 1.8:1, the ratio (z :y) is within a range of 0.4 to1.4:1 and the oxygen deficit amount (d) is within a range of from 3×10⁻⁵to 1×10⁻¹ times the value of (x+3y/2+3z/2).
 2. An electro-conductiveoxide represented by the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is at least one element selected from the group consistingof magnesium and zinc, M(2) is at least one element selected from thegroup consisting of aluminium and gallium, the ratio (x:y) is within arange of 0.2 to 1.8:1, the ratio (z:y) is within a range of 0.4 to 1.4:1and the oxygen deficit amount (d) is within a range of from 0 to 1×10⁻¹times the value of (x+3y/2+3z/2), in which a part of at least one ofM(1), M(2) and In is replaced with one or more other elements, theelements replacing M(1) are of di- or higher valence and the elementsreplacing M(2) and In are of tri- or higher valence.
 3. Anelectro-conductive oxide of claim 2 wherein the oxygen deficit amount(d) and the replaced amounts of M(1), M(2) and In are selected so thatthe oxide has an amount of carrier electrons of from 1×10¹⁸ /cm³ to1×10²² /cm³.
 4. An electro-conductive oxide represented by the generalformula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is at least one element selected from the group consistingof magnesium and zinc, M(2) is at least one element selected from thegroup consisting of aluminium and gallium, the ratio (x:y) is within arange of 0.2 to 1.8:1, the ratio (z:y) is within a range of 0.4 to 1.4:1and the oxygen deficit amount (d) is within a range of from 0 to 1×10⁻¹times the value of (x+3y/2+3z/2), wherein said electroconductive oxideis implanted with cations having a smaller ionic radius than the atomsof the oxide, and wherein the oxygen deficit amount (d) and the amountof implanted cations are selected so that the electroconductive oxidehas an amount of carrier electrons of from 1×10¹⁸ /cm³ to 1×10²² /cm³.5. An electro-conductive oxide of claim 1 which is represented by thegeneral formula: InGaZn₀.5 O₃.5-d, which corresponds to the generalformula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is zinc, M(2) is gallium, x is 0.5, y is 1 and z is
 1. 6.An electro-conductive oxide of claim 2 which is represented by thegeneral formula: InGaZn₀.5 O₃.5.spsb.-d, which corresponds to thegeneral formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is zinc, M(2) is gallium, x is 0.5, y is 1 and z is
 1. 7.An electro-conductive oxide of claim 4 which is represented by thegeneral formula: InGaZn₀.5 O₃.5.spsb.-d, which corresponds to thegeneral formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is zinc, M(2) is gallium, x is 0.5, y is 1 and z is
 1. 8.An electro-conductive oxide of claim 1 which is represented by thegeneral formula: InAlZn₀.5 O₃.5.spsb.-d, which corresponds to thegeneral formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is zinc, M(2) is alminium, x is 0.5, y is 1 and z is
 1. 9.An electro-conductive oxide of claim 2 which is represented by thegeneral formula: InAlZn₀.5 O₃.5.spsb.-d, which corresponds to thegeneral formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is zinc, M(2) is aluminium, x is 0.5, y is 1 and z is 1.10. An electro-conductive oxide of claim 4 which is represented by thegeneral formula: InAlZn₀.5 O₃.5.spsb.-d, which corresponds to thegeneral formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein M(1) is zinc, M(2) is aluminium, x is 0.5, y is 1 and z is 1.11. An electro-conductive oxide of claim 1 which is represented by thegeneral formula: M(1)M(2)InO₄.spsb.-d, which corresponds to the generalformula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein x is 1, y is 1 and z is
 1. 12. An electro-conductive oxide ofclaim 2 which is represented by the general formula:M(1)M(2)InO₄.spsb.-d, which corresponds to the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein x is 1, y is 1 and z is
 1. 13. An electro-conductive oxide ofclaim 4 which is represented by the general formula:M(1)M(2)InO₄.spsb.-d, which corresponds to the general formula:

    M(1).sub.x M(2).sub.y In.sub.z O.sub.(x+.spsb.3.sub.y/.spsb.2.sub.+.spsb.3.sub.z/.spsb.2.sub.)-d

wherein x is 1, y is 1 and z is 1.